A substrate such as a semiconductor wafer on which a silicon oxide film, a nitride film, or the like is formed as a configuration of the substrate using a base material composed of silicon or the like is known. A contaminant such as metal or an organic material may contaminate the material constituting the semiconductor substrate in a manufacturing process, and even a small amount of the contaminant significantly lowers semiconductor characteristics. For this reason, there is a demand for a technology of analyzing a small amount of a contamination source included in the substrate as an analysis object.
In the analysis of a small amount of the contamination source included in the substrate, for example, there is known a method of decomposing a constitutional film of a substrate by etching, ejecting an analysis recovery liquid onto the substrate after etching, moving the recovery liquid on the substrate, shifting the analysis object into the liquid, collecting the analysis object, and analyzing the recovery liquid qualitatively and quantitatively by inductively coupled plasma (ICP) analysis or the like.
A vapor-phase decomposition method using etching gas generated by bubbling a mixed acid solution formed of nitric acid or hydrogen peroxide mixed with a hydrofluoric acid or the like is known as etching of a constitutional film of a substrate, and an apparatus that includes a chamber in which a substrate is arranged and that is capable of introducing etching gas into the chamber is used as an etching apparatus for the above-described method. For example, as disclosed in Patent Document 1, etching gas can be supplied from an etching gas introduction port provided in a chamber (FIG. 1 in Patent Document 1). The etching gas arbitrarily flows to the space in the chamber, and only gas contacted a substrate surface among the flown etching gas contributes to etching of the substrate. In this way, a flow direction of the etching gas is not particularly controlled in the chamber, but since etching gas having a relative low etching performance such as a mixed acid solution of hydrofluoric acid is used as the etching gas, it is possible to etch only a formed film of interest such as an oxide film or a nitride film.
Here, in the substrate analysis, as a formed film of which contamination source needs to be analyzed, it is also necessary to analyze a formed film relatively difficult to decompose such as polysilicon or a substrate itself (bulk silicon) in addition to a formed film relatively easy to decompose such as the above-described oxide film or nitride film. In such analysis of the polysilicon or the substrate itself, etching gas having a high etching performance is necessary, and, for example, a technology using a solution formed of ozone water added to a mixed acid solution (Patent Document 2) and a technology using vapor of hydrogen fluoride and ozone-containing gas (Patent Document 1) have been proposed.